Flexible display apparatus having a well and a discontinuous region in an encapsulation layer

ABSTRACT

A flexible display device including a well structure. An organic light-emitting element including a pixel electrode, an organic light-emitting layer, and a common electrode is disposed on a substrate. A bank layer is disposed on the pixel electrode, and is disposed to open at least a part of the pixel electrode. Further, at least one well structure is disposed on the bank layer. The well structure disposed on the bank layer can reduce or minimize a delamination phenomenon of an encapsulation layer which can occur due to compressive and tensile stress caused by bending of the flexible display device.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to Korean Patent Application No.10-2018-0145003, filed Nov. 22, 2018, which is hereby incorporated byreference for all purposes as if fully set forth herein.

BACKGROUND Technical Field

The present disclosure generally relates to a flexible display device.

Description of the Related Art

Display devices can be divided into liquid crystal displays devices inwhich liquid crystals are used to produce an image, and organiclight-emitting diode display devices in which an organic light-emittinglayer is used to do so. Moreover, a demand for flexible or foldabledisplay devices instead of flat panel display devices has recently beenrising.

The organic light-emitting diode display devices in which an organiclight-emitting element is used as a pixel for producing an image do notrequire a separate light source compared to the liquid crystal displaydevices. As a result, the organic light-emitting diode display devicescan be made lighter and thinner, and can be fabricated as flexibledisplay devices. These organic light-emitting diode display devices arenot only advantageous in the aspect of power consumption due tolow-voltage driving, but also are excellent in hue realization, responsespeed, viewing angle, and contrast ratio (CR). Thus, researches intoapplication of flexible display devices have been actively conducted.

The organic light-emitting diode display devices include a substrateincluding driving elements formed of a thin film transistor, pixelelectrodes connected to the driving elements, an organic light-emittinglayer, and a common electrode, which are formed in order, and areconfigured such that the organic light-emitting layer is driven to emitlight by driving signals of the driving elements.

The organic light-emitting layer emits light when electrons and holesinjected from the pixel electrodes and the common electrode meet at theorganic light-emitting layer and form excitation. The organiclight-emitting layer is especially sensitive to moisture and oxygen. Toprevent permeation of the moisture and the oxygen, the organiclight-emitting layer includes one or more encapsulation layers aboveorganic light-emitting elements.

A thin-film encapsulation technique for alternately laminating inorganicand organic materials to seal the organic light-emitting elements may beused for the encapsulation layer. A material such as aluminum oxide(AlOx) or silicon nitride (SiNx) able to secure an excellent barriercharacteristic with a small thickness is mainly used for a thin-filmencapsulation layer formed of an inorganic material.

In the flexible display devices, a structure, in which the inorganic andorganic materials of the aforementioned encapsulation layer arealternately laminated (or deposited), is easily damaged by repetition ofcompressive stress and tensile stress. For this reason, there may be aproblem related to reliability and lifetime of the flexible displaydevices in which an organic light-emitting element is used as a pixel.

BRIEF SUMMARY

In the flexible display devices in which an organic light-emittingelement is used as a pixel, as described above, delamination or cracksmay occur in the light emitting layer or the thin-film encapsulationlayer when the display device is repetitively bent and unbent.

Thus, the inventors of the present disclosure have invented a newstructure of the flexible display device that can reduce the stress suchas the compressive stress and the tensile stress in an environment thatthe flexible display device is exposed to such stress.

One or more embodiments of the present disclosure provide a flexibledisplay device which is less likely to have cracks in an encapsulationlayer caused by the stress such as repetitive bending and unbending.

One or more embodiments of the present disclosure provide a flexibledisplay device that is less likely have damage to an encapsulation layercaused by the stress such as repetitive bending and unbending andthereby increases reliability and lifetime of the flexible display.

The object of the present disclosure is not limited to theaforementioned description, and other objects not explicitly disclosedherein will be clearly understood by a person having ordinary skill inthe art to which the present disclosure pertains from the descriptionprovided hereinafter.

According to at least one embodiment of the present disclosure, aflexible display device in which reliability of a service life onbending or the like is provided. A driving element is disposed on aflexible substrate along with a planarization layer and a bank layer. Anorganic light-emitting element is disposed on the planarization layer,and the bank layer that opens the organic light-emitting element isdisposed. The organic light-emitting element is covered by anencapsulation layer including a first encapsulation layer, a secondencapsulation layer, and a third encapsulation layer, and the bank layerincludes at least one well structure, so that cracks or a delaminationphenomenon that can occur in the encapsulation layer in a flexingenvironment can be reduced.

According to at least one embodiment of the present disclosure, theflexible display device includes at least one well structure on the banklayer. The well structure can be used to reduce damage caused by bendingstress of the encapsulation layer.

Further, according to at least one embodiment of the present disclosure,at least one well structure and the second encapsulation layer trappedby the well structure have an effect of more effectively reducing damagecaused by bending stress and can further improve reliability of aservice life.

The effects of the present disclosure are not limited to the effectsdescribed above, and other undescribed effects will be clearlyunderstood to those skilled in the art from the following description.

The contents of the disclosure which are described in the problem to besolved, the solution to the problem, and the effects do not specifyessential features of the claims, and thus the scope of the claims isnot limited by the matters described in the contents of the disclosure.

DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The above and other objects, features, and advantages of the presentdisclosure will be more clearly understood from the following detaileddescription, taken in conjunction with the accompanying drawings, inwhich:

FIGS. 1A to 1C are schematic views illustrating a flexing environmentaccording to an embodiment of the present disclosure;

FIG. 2 is a schematic sectional view illustrating cracks and adelamination phenomenon that occur in a flexible display device, takenalong line A-A′ of FIG. 1A;

FIGS. 3A and 3B are schematic views illustrating cracks, a delaminationphenomenon, and bending stress that occur in the flexible displaydevice;

FIG. 4 is a schematic view illustrating a flexible display deviceincluding a well structure according to one or more embodiments of thepresent disclosure; and

FIG. 5 is a schematic view illustrating a flexible display deviceincluding dams and a well structure according to one or more embodimentsof the present disclosure.

FIG. 6 a schematic view illustrating the flexible display deviceincluding the dams and the well structure.

DETAILED DESCRIPTION

The advantages and features of the present disclosure and methods of therealization thereof will be apparent with reference to the accompanyingdrawings and detailed descriptions of the embodiments. The presentdisclosure should not be construed as being limited to the embodimentsset forth herein and may be embodied in many different forms. Rather,these embodiments are provided so that the present disclosure will bethorough and complete, and will fully convey the scope of the presentdisclosure to a person having ordinary skill in the art.

The shapes, sizes, ratios, angles, numbers, and the like, inscribed inthe drawings to illustrate exemplary embodiments are illustrative only,and the present disclosure is not limited to the embodiments illustratedin the drawings. Throughout this document, the same reference numeralsand symbols will be used to designate the same or like components. Inthe following description of the present disclosure, detaileddescriptions of known functions and components incorporated into thepresent disclosure will be omitted in the situation in which the subjectmatter of the present disclosure may be rendered unclear thereby. Itwill be understood that the terms “comprise,” “include,” “have,” and anyvariations thereof used herein are intended to cover non-exclusiveinclusions unless explicitly described to the contrary. Descriptions ofcomponents in the singular form used herein are intended to includedescriptions of components in the plural form, unless explicitlydescribed to the contrary.

In the analysis of a component, it shall be understood that an errorrange is included therein, even in the situation in which there is noexplicit description thereof.

When spatially relative terms, such as “on,” “above,” “under,” “below,”and “on a side of,” are used herein for descriptions of relationshipsbetween one element or component and another element or component, oneor more intervening elements or components may be present between theone and other elements or components, unless a term, such as “directly,”is used.

In addition, terms, such as “first” and “second” may be used herein todescribe a variety of components. It should be understood, however, thatthese components are not limited by these terms. These terms are merelyused to discriminate one element or component from other elements orcomponents. Thus, a first component referred to as first hereinafter maybe a second component within the spirit of the present disclosure.

The features of one or more embodiments of the present disclosure may bepartially or entirely coupled or combined with each other and may workin concert with each other or may operate in a variety of technicalmethods. In addition, respective one or more embodiments may be carriedout independently or may be associated with and carried out in concertwith other embodiments.

With regard to various configurations of an organic light-emitting diodedisplay device able to reduce or minimize a delamination phenomenon ofan organic light-emitting layer or an encapsulation layer according toone or embodiments of the present disclosure, various embodiments of thepresent disclosure will be described below in detail with reference tothe attached drawings.

FIGS. 1A to 1C are schematic views illustrating a flexing environmentaccording to one or more embodiments of the present disclosure.Referring to FIGS. 1A to 1C, a flexible display device 100 may include asubstrate 110 as a base, and various components disposed on thesubstrate 110. The substrate 110 may include a plurality of pixelregions and driving elements formed of a thin film transistor located oneach pixel region, and may be formed of a plastic material having aflexible characteristic.

The plastic material of the substrate 110 may include, but not limitedto, polyethersulfone, polyacrylate, polyetherimide, polyethylenenaphthalate, polyethylene terephthalate, polyphenylene sulfide,polyallylate, polyimide, polycarbonate, or the like, and may be variousmaterials of which a flexible substrate is formed.

As illustrated in FIG. 1A, the flexible display device 100 using theaforementioned substrate 110 as the base can be rolled, bent, or folded.As illustrated in FIG. 1B, the flexible display device 100 may beutilized as a rollable or extremely curved display device. Further, asillustrated in FIG. 1C, the flexible display device 100 may be curved orbent in various directions rather than one direction.

A phenomenon in which the flexible display device that is curved,extremely bent or unbent in this way is, for example, delaminated easilybecause a bonding force between the components is reduced by bendingstress. A concrete example of defects occurring in a flexing environmentwill be described.

FIG. 2 is a schematic sectional view illustrating cracks and adelamination phenomenon that occur in the flexible display device, takenalong line A-A′ of FIG. 1A.

Two typical defects occurring in the flexible display device will bedescribed with reference to FIG. 2.

The substrate 110 may be a flexible substrate 110, and the followingelements for constituting the organic light-emitting diode displaydevice may be disposed on the substrate 110.

A driving element 120 comprised of a source electrode 121, a drainelectrode 122, an active electrode 124, and a gate electrode 123 isdisposed on the substrate 110. The active electrode 124 is disposed tocorrespond to the gate electrode 123, and the source electrode 121 andthe drain electrode 122 are electrically connected to the activeelectrode 124 through contact holes passing through an insulating layer111, and the gate electrode 123 and the active electrode 124 areinsulated by the insulating layer 111.

A passivation layer 112 and a planarization layer 113 are disposed onthe source electrode 121 and the drain electrode 122, and a pixelelectrode 131 is disposed on the planarization layer 113.

The planarization layer 113 may include a material having excellent heatresistance, such as an acrylic resin, an epoxy resin, a phenol resin, apolyamide resin, a polyimide resin, an unsaturated polyester resin, apolyphenylene resin, a polyphenylene sulfide resin, benzocyclobutene, orthe like.

The passivation layer 112 may include a single layer or a plurality oflayers, is formed of silicon oxide (SiO₂) or silicon nitride (SiNx) thatis an inorganic insulating material in order to interrupt inflow ofmoisture or oxygen, or may include an organic material such as apolymer.

An organic light-emitting element 130 comprised of the pixel electrode131, an organic light-emitting layer 132, and a common electrode 133 isdisposed on the planarization layer 113. Further, a bank layer 114 thatopens the pixel electrode 131 is disposed on the planarization layer113.

The pixel electrode 131 is connected to the drain electrode 122 of thedriving element 120, which is the thin film transistor, through avia-hole that passes through the planarization layer 113 and thepassivation layer 112. In particular, the pixel electrode 131 may beformed of a material having high reflectivity in order to reflect lightemitted from the organic light-emitting layer 132.

The aforementioned pixel electrode 131 may be formed of, for example, atleast one of molybdenum (Mo), aluminum (Al), silver (Ag), chromium (Cr),gold (Au), titanium (Ti), nickel (Ni), neodymium (Nd), or copper (Cu),or an alloy including at least one of these materials.

The bank layer 114 may be formed of, for example, at least one ofpolyimide, photo acryl, or benzocyclobutene (BCB) that an organicinsulating material having a general photosensitive characteristic, ormay be formed of a black resin that is a material showing black.

The organic light-emitting layer 132 is provided on the pixel electrode131. The organic light-emitting layer 132 may be an organiclight-emitting layer that is configured to emit red, green, or bluelight, or may be an organic light-emitting layer 132 that emits whitelight or UV light.

The organic light-emitting layer 132 may be disposed on a partial regionthat corresponds to the pixel electrode 131, or may be disposed on anentire region that corresponds to the pixel electrode 131 by variousprocesses of disposing the organic light-emitting layer 132.

The common electrode 133 is disposed on the organic light-emitting layer132, and an encapsulation layer 140 is disposed on the common electrode133. The common electrode 133 may be formed of a transparent conductivematerial such as ITO, and the encapsulation layer 140 may have astructure in which an inorganic material and an organic material arealternately disposed.

As illustrated in FIG. 2, the encapsulation layer 140 may have astructure in which an inorganic material and an organic material arealternately disposed. The aforementioned encapsulation layer 140 mayinclude a first encapsulation layer 141, a second encapsulation layer142, and a third encapsulation layer 143.

For example, the first encapsulation layer 141 and the thirdencapsulation layer 143 may be encapsulation layers formed of aninorganic material, and the second encapsulation layer 142 may be anencapsulation layer formed of an organic material, such that theinorganic material and the organic material are alternately disposed inthe encapsulation layer 140.

Meanwhile, an inverted tapered structure 151 and a spacer 152 may bedisposed on the bank layer 114. The inverted tapered structure 151disposed on the bank layer 114 may be an inverted tapered structure, atleast one side of which has an inverted tapered shape in order to reduceor minimize delamination between the organic light-emitting layer 132 orthe common electrode 133 and the first encapsulation layer 141.

The spacer 152 has a structure that supports a mask such as a fine metalmask (FMM) in a process of disposing the organic light-emitting layer132, and serves to prevent the other components from generating foreignmaterials due to the mask.

Hereinafter, two typical kinds of defects that can occur in the flexibledisplay device will be described with further reference to FIGS. 3A and3B.

FIGS. 3A and 3B are schematic views illustrating cracks, a delaminationphenomenon, and bending stress that occur in the flexible displaydevice.

Causes and effects of first and second defects E1 and E2 illustrated inFIG. 2 will be described with reference to FIGS. 3A and 3B as follows.

The first defect E1 may be caused by the tensile stress which maydamages the third encapsulation layer 143 as illustrated in FIG. 3A. Theencapsulation 143 protects the flexible display device from moisture andoxygen. As a result of the first defect E1, a moisture (or oxygen)permeation path can be created as illustrated in FIG. 3A. In otherwords, in the case of the tensile stress, intermolecular bonding forcesof the first to third encapsulation layers 141 to 143 are weakened dueto repeated tensile stress, and cracks occur, so that the moisture (orany fluids, gases, etc., such as oxygen) permeation path occurs.

In the case of the second defect E2, interlayer bonding forces betweenthe first to third encapsulation layers 141 to 143 are weakened bycompressive stress. This results in a phenomenon in which a concentratedpressure does not find an exit and is concentrated on a portion at whichthe interlayer bonding force is weak, and delamination occurs.

In this way, the first defect E1 and the second defect E2 can occur in acombined form. This is because the cracks and the delamination can occurtogether due to the repeated stress by which the intermolecular andinterlayer bonding forces are weakened, compression and tension areadded to a portion at which the defect occurs once, and a degree of thedefect becomes worse.

FIG. 4 is a schematic view illustrating a flexible display deviceincluding a well structure according to another embodiment of thepresent disclosure.

Referring to FIG. 4, a bank layer 114 may be disposed including a wellstructure 160. Due to the well structure 160 disposed in the bank layer114, the first to the third encapsulation layers 141 to 143 of anencapsulation layer 140 have groove shapes. The well structure 160 maybecome a buffer space that can effectively cope with tensile andcompressive stress applied to the encapsulation layer 140. In otherwords, the well structure 160 allows at least some portion of theencapsulation layer 140 extending into at least some portion of otherlayer or other layers under the encapsulation layer 140, creating anuneven portion (or rough portion) in the encapsulation layer 140 whichcan provide more tolerance against the stress than a flat portion alone.

In some embodiments, the well structure 160 may be at least partiallydefined by the bank layer 114, for example, at least a portion of thewell structure 160 may include a cavity or well shape which extends intoor through the bank layer 114. In some embodiments, the well structure160 extends at least partially into the underlying bank layer 114. Insome embodiments, the well structure 160 extends through the bank layer114 to at least a level of a surface (e.g., an upper surface) of theplanarization layer 113. In some embodiments, the well structure 160extends through the bank layer 114 and at least partially into theplanarization layer 113 (e.g., as shown in FIG. 4).

Since the encapsulation layer 140 has a groove shape due to theaforementioned well structure 160, a total internal reflection patterncan be generated, and an optical out-coupling effect can be produced onlight emitted from an organic light-emitting element 130. Thus,improvement of the optical efficiency of the flexible display device 100can be provided.

Meanwhile, since the encapsulation layer 140 has a groove shape due tothe well structure 160, an effect of preventing the light emitted fromthe organic light-emitting element 130 from interfering with lightemitted from other pixels can be produced. For this reason, an effectthat can reduce or minimize a color mixture is obtained.

The well structure 160 may be disposed around a pixel, and may bedisposed to extend at least partially into a planarization layer 113,and in some embodiments, the well structure 160 may extend to or atleast partially into a passivation layer 112 in order to increase adepth thereof, as illustrated in FIG. 6.

Due to the groove shape caused by the well structure 160, an uppersurface of the encapsulation layer may have a groove shape (or a trenchpattern).

FIG. 5 is a schematic view illustrating a flexible display deviceincluding dams and a well structure according to one or more embodimentsof the present disclosure.

Referring to FIG. 5, a well structure 160 further includes at least twodams 150. The well structure 160 including at least two dams 150provides a discontinuous section or gap in which the secondencapsulation layer 142 is discontinuous or disconnected. The dams 150are disposed such that heights of the dams 150 are higher than the sumof heights (or thicknesses) of the first encapsulation layer, the secondencapsulation layer, and the third encapsulation layer 141, 142, and143, and thereby the second encapsulation layer 142 has thediscontinuous section due to the two dams 150. While FIG. 5 illustratesonly a portion of the third encapsulation layer 143 disposed between thedams 150, i.e., with no portion of the second encapsulation layer 142disposed in the discontinuous section, in some embodiments, someseparate portion of the second encapsulation layer 142 may be locatedbetween the two dams 150.

The second encapsulation layer 142 that is discontinuous due to the dams150 is configured to flexibly cope with tensile and compressive stressto reduce or minimize occurrence of cracks or the like that can occur ina flexible display device.

When the tensile stress and the compressive stress occur repetitively,the second encapsulation layer 142 can have a structure that issubjected to compression and tension by the aforementioned stress on thebasis of the second encapsulation layer 142 trapped by the wellstructure 160.

A part of the second encapsulation layer 142 in which the well structure160 is disposed has a lower height than the other part of the secondencapsulation layer 142 which is located therearound, and a buffer spaceof the tensile and compressive stress applied to the parts of the secondencapsulation layer 142 which have heights different from each other isprovided.

For example, the height of the first encapsulation layer 141 may be 1μm, and a height of a bank layer 114 may be about 2 μm. The height ofthe second encapsulation layer 142 may be about 5 μm, and the height ofthe third encapsulation layer 143 may be about 1 μm. Here, the firstencapsulation layer 141 and the third encapsulation layer 143 may bedisposed on the dams 150. Therefore, in comparison with the heights ofthe dams 150 and the height of the second encapsulation layer 142, aheight about 1.5 μm of an inverted tapered structure 151 and a heightabout 2.3 μm of a spacer 152 plus the height about 2 μm of the banklayer 114 makes about 5.8 μm, and thus the heights of the dams 150 maybe higher than the height about 5 μm of the second encapsulation layer142. As a result, the dams 150 can be disposed to be higher than theencapsulation layer 140.

When each of the dams 150 having the heights as described above isconfigured using the components such as the inverted tapered structure151 and the spacer 152 disposed on the bank layer 114, the dams 150having a higher height than the aforementioned encapsulation layer 140can be disposed.

The well structure 160 together with the two dams 150 can create anuneven portion (or rough portion) in the encapsulation layer 140 whichcan provide more tolerance against the stress than a flat portion alone.In some embodiments, one or more portions of the first encapsulationlayer 141 and the third encapsulation layer 143 on the well structure160 may be adjoining or even in contact with each another. For example,as shown in FIG. 5, portions of the first encapsulation layer 141 andthe third encapsulation layer 143 may be adjoining or in contact withone another along one or more surfaces (e.g., outer surfaces) of thedams 150 of the well structure 160.

The foregoing descriptions and the accompanying drawings have beenpresented in order to explain certain principles of the presentdisclosure by way of example. A person having ordinary skill in the artto which the present disclosure relates could make various modificationsand variations without departing from the principle of the presentdisclosure. The foregoing embodiments disclosed herein shall beinterpreted as being illustrative, while not being limitative, of theprinciple and scope of the present disclosure.

The various embodiments described above can be combined to providefurther embodiments. Further changes can be made to the embodiments inlight of the above-detailed description. In general, in the followingclaims, the terms used should not be construed to limit the claims tothe specific embodiments disclosed in the specification and the claims,but should be construed to include all possible embodiments along withthe full scope of equivalents to which such claims are entitled.Accordingly, the claims are not limited by the disclosure.

What is claimed is:
 1. A flexible display device, comprising: a banklayer and an organic light-emitting element disposed on a flexiblesubstrate; and an encapsulation layer including a first encapsulationlayer, a second encapsulation layer, and a third encapsulation layerthat cover the organic light-emitting element, wherein the bank layer atleast partially defines at least one well structure, and wherein thesecond encapsulation layer includes a first portion and a second portionthat are separated from each other resulting in the second encapsulationlayer not being continuous and having the first portion and the secondportions spaced apart from each other; wherein at least two dams aredisposed to disconnect the first portion from the second portion, and athird portion of the second encapsulation layer in the well structurehas a lower height than the first portion.
 2. The flexible displaydevice according to claim 1, wherein the third portion is separated fromthe first portion and the second portions of the second encapsulationlayer.
 3. A flexible display device, comprising: a plurality of organiclight-emitting element disposed on a flexible substrate; a bank layer onthe flexible substrate; and an encapsulation layer including a firstencapsulation layer, a second encapsulation layer, and a thirdencapsulation layer that cover the organic light-emitting element,wherein the bank layer at least partially defines at least one wellstructure that is located between two light-emitting elements of theplurality of light emitting elements, and wherein the secondencapsulation layer includes a first portion and a second portion thatare separated from each other resulting in the second encapsulationlayer not being continuous and having the first portion and the secondportion spaced apart from each other; wherein portions of the first andthe third encapsulation layers on the well structure are adjoined toeach other.
 4. The flexible display device according to claim 1, furthercomprising a planarization layer on the flexible substrate, wherein thewell structure extends at least partially into the planarization layer.5. The flexible display device according to claim 4, wherein theplanarization layer is discontinuous at a location corresponding to thewell structure.
 6. The flexible display device according to claim 1,further comprising a passivation layer on the flexible substrate,wherein the well structure extends at least partially into thepassivation layer.
 7. A flexible display device, comprising: a banklayer and an organic light-emitting element disposed on a flexiblesubstrate; and an encapsulation layer including a first encapsulationlayer, a second encapsulation layer, and a third encapsulation layerthat cover the organic light-emitting element, wherein the bank layer atleast partially defines at least one well structure, and wherein thesecond encapsulation layer includes a first portion and a second portionthat are separated from each other resulting in the second encapsulationlayer not being continuous and having the first portion and the secondportion spaced apart from each other; wherein the well structureincludes at least two dams spaced apart from each other, and a first damand a second dam of the at least two dams are located adjacent to thefirst portion and the second portion, respectively, such that a part ofthe well structure is located between the first dam and the second damin a cross-sectional view.
 8. The flexible display device according toclaim 7, wherein heights of the dams are higher than or equal to the sumof heights of the first encapsulation layer, the second encapsulationlayer, and the third encapsulation layer.
 9. The flexible display deviceaccording to claim 7, wherein each of the at least two dams includes aninverted tapered structure and a spacer on the bank layer.
 10. Theflexible display device according to claim 1, wherein an upper surfaceof the encapsulation layer has a groove shape due to the well structure.